Android中ListView动态加载数据

1. 引言：

为了提高ListView的效率和应用程序的性能，在Android应用程序中不应该一次性加载ListView所要显示的全部信息，而是采取分批加载策略，随着用户的滑动，动态的从后台加载所需的数据，并渲染到ListView组件中，这样可以极大的改善应用程序的性能和用户体验。

2. 交互：

进入ListView组件，首先预加载N条记录，当用户滑动到最后一条记录显示加载提示信息，并从后台加载N条数据，接着渲染UI界面。

3. 效果图：

4. 程序实现：

package com.focus.loading;
import android.app.ListActivity;
import android.os.Bundle;
import android.os.Handler;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.BaseAdapter;
import android.widget.LinearLayout;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.LinearLayout.LayoutParams;
public class ListViewLoadingActivity extends ListActivity implements
		OnScrollListener {
	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		/**
		 * "加载项"布局，此布局被添加到ListView的Footer中。
		 */
		mLoadLayout = new LinearLayout(this);
		mLoadLayout.setMinimumHeight(60);
		mLoadLayout.setGravity(Gravity.CENTER);
		mLoadLayout.setOrientation(LinearLayout.HORIZONTAL);
		/**
		 * 向"加载项"布局中添加一个圆型进度条。
		 */
		ProgressBar mProgressBar = new ProgressBar(this);
		mProgressBar.setPadding(0, 0, 15, 0);
		mLoadLayout.addView(mProgressBar, mProgressBarLayoutParams);
		/**
		 * 向"加载项"布局中添加提示信息。
		 */
		TextView mTipContent = new TextView(this);
		mTipContent.setText("加载中...");
		mLoadLayout.addView(mTipContent, mTipContentLayoutParams);
		/**
		 * 获取ListView组件，并将"加载项"布局添加到ListView组件的Footer中。
		 */
		mListView = getListView();
		mListView.addFooterView(mLoadLayout);
		/**
		 * 组ListView组件设置Adapter,并设置滑动监听事件。
		 */
		setListAdapter(mListViewAdapter);
		mListView.setOnScrollListener(this);
	}
	public void onScroll(AbsListView view, int mFirstVisibleItem,
			int mVisibleItemCount, int mTotalItemCount) {
		mLastItem = mFirstVisibleItem + mVisibleItemCount - 1;
		if (mListViewAdapter.count > mCount) {
			mListView.removeFooterView(mLoadLayout);
		}
	}
	public void onScrollStateChanged(AbsListView view, int mScrollState) {

		/**
		 * 当ListView滑动到最后一条记录时这时，我们会看到已经被添加到ListView的"加载项"布局， 这时应该加载剩余数据。
		 */
		if (mLastItem == mListViewAdapter.count
				&& mScrollState == OnScrollListener.SCROLL_STATE_IDLE) {
			if (mListViewAdapter.count <= mCount) {
				mHandler.postDelayed(new Runnable() {
					@Override
					public void run() {
						mListViewAdapter.count += 10;
						mListViewAdapter.notifyDataSetChanged();
						mListView.setSelection(mLastItem);
					}
				}, 1000);
			}
		}
	}
	class ListViewAdapter extends BaseAdapter {
		int count = 10;
		public int getCount() {
			return count;
		}
		public Object getItem(int position) {
			return position;
		}
		public long getItemId(int position) {
			return position;
		}
		public View getView(int position, View view, ViewGroup parent) {
			TextView mTextView;
			if (view == null) {
				mTextView = new TextView(ListViewLoadingActivity.this);
			} else {
				mTextView = (TextView) view;
			}
			mTextView.setText("Item " + position);
			mTextView.setTextSize(20f);
			mTextView.setGravity(Gravity.CENTER);
			mTextView.setHeight(60);
			return mTextView;
		}
	}
	private LinearLayout mLoadLayout;
	private ListView mListView;
	private ListViewAdapter mListViewAdapter = new ListViewAdapter();
	private int mLastItem = 0;
	private int mCount = 41;
	private final Handler mHandler = new Handler();
	private final LayoutParams mProgressBarLayoutParams = new LinearLayout.LayoutParams(
			LinearLayout.LayoutParams.WRAP_CONTENT,
			LinearLayout.LayoutParams.WRAP_CONTENT);
	private final LayoutParams mTipContentLayoutParams = new LinearLayout.LayoutParams(
			LinearLayout.LayoutParams.WRAP_CONTENT,
			LinearLayout.LayoutParams.WRAP_CONTENT);
}